Method and apparatus for shifting speeds in a fluid-actuated motor

Abstract

A method and apparatus for changing the speed of a drill bit down hole in a fluid-actuated motor, including a positive displacement motor and a hydraulic motor, is disclosed. The apparatus comprises a bypass valve installed in the motor for controlling flow through and around the power section of the motor. When closed, the bypass valve forces all fluid to flow through the power section of the motor, imparting maximum speed to the drill bit. When opened, a portion of the fluid flow is allowed to flow around the power section of the motor, thereby reducing the speed of the drill bit. The bypass valve may be opened or closed mechanically, electrically, hydraulically, pneumatically, or by any other means, including a removable plug.

Description

FIELD OF THE INVENTION [0001] The present invention generally relates to fluid-actuated motors, including positive displacement motors, known as Moineau pump-type drilling motors, and hydraulic motors, and specifically to a fluid-actuated motor having a variable rotor bypass valve installed therein to alter the rotational speed of the drill bit without the need for the motor to be removed from the well. BACKGROUND OF THE INVENTION [0002] In the oil drilling industry, there are two traditional methods of drilling an oil well. One is to attach a drill bit at the end of a drill string, apply downward pressure, and rotate the drill string from the surface so that the drill bit cuts into a formation. The problem with this method is that as the hole becomes deeper and the drill string becomes longer, the frictional forces due to the rotation of the drill string down hole increase, especially in deviated and horizontal wells. [0003] The second method is to place a motor down hole near the ...

AI Technical Summary

Benefits of technology

[0007] The present invention allows an operator to change the rotational speed of the drill bit by causing a portion of the fluid that is pumped through the drill string to bypass that part of the power section of a motor that imparts rotational motion on the drill bit without passing any of the fluid outside of the drill string. This is accomplished by means of a bypass valve installed inside, above, or below the power section of the motor.

[0008] The bypass valve separates the fluid flow through the power section into two paths. One path is directed through that part of the power section that causes the drill bit to rotate while the other path is directed around it. When the bypass valve acts to cause all of the fluid to flow through the power section of a motor, the drill bit will rotate at maximum speed. When the bypass valve acts to bypass a portion of the fluid through a port in the power section, the drill bit will rotate at a slower speed. The actual internal geometry of the fluid flow through the power section in conjunction with the fluid flow pressure maintained at the mud pump determines the actual speed of rotation. After the bypass valve separates the fluid into two flow paths, the flow is recombined inside the motor before it is channeled to the drill bit. This allows all of the fluid that flows down the drill string to cool the drill bit and to circulate the cuttings back up to the surface without any detrimental impact on system performance.

[0016] In even another embodiment, the amount of fluid that flows through the bypass valve when open is controllably selected by the size of a replaceable nozzle that installs inside the cam. The replaceable nozzle is configured to restrict a certain amount of flow through the cam and the housing when the bypass valve is open, thereby allowing a drilling operator to pre-set the speed of the drill bit.

[0017] In still another embodiment, the bypass valve may also be configured to open and close automatically based upon the type of formation encountered during drilling. When the drill bit encounters a harder formation, more weight is needed to press through it. The increased weight increases the friction on the bit and the pressure experienced by the motor. The bypass valve can be configured to respond to the increased pressure by, for example, opening one or more spring-loaded outlet valves. When the increased pressure experienced by the motor overcomes the closing forces of the spring-loaded outlet valves, the outlet valves open, diverting a portion of the fluid flow around the power section of the rotor and slowing the speed of the drill bit. The spring-loaded outlet valves may be configured to adjust to the amount of pressure experienced by the motor, allowing the amount of fluid to flow around the power section of the motor to be a function of the pressure experienced by the motor.

Problems solved by technology

In underbalanced drilling, the fluid pumped down the drill string is composed of a mixture of fluid and gas.

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